The invention relates to an exhaust manifold for mounting on a cylinder head of an internal combustion engine.
In EP 0 709 557 A1, an exhaust-tube manifold is described in a design as used in very many internal combustion engines. Each exhaust tube is welded to a flange which is then screwed onto the cylinder head of the internal combustion engine. The exhaust tubes open in a known manner into a collector tube, which continues into an exhaust pipe.
Known exhaust manifolds of this type are disadvantageously very heavy and expensive and have the further disadvantage that because of their large mass they take away very large amounts of heat from the exhaust gas passed into them. This reduces the temperature of the exhaust gas, which has the effect that the catalytic converter arranged in the exhaust pipe has very poor efficiency, particularly during starting of the internal combustion engine.
In order to improve the efficiency and the light-off performance of the catalytic converter, according to one prior art which is known from practice, exhaust manifolds having xe2x80x9cair gap insulationxe2x80x9d have been developed, in which a housing and a gas-conducting pipe arranged in the housing are provided.
Even here, however, the relatively high mass and, in particular, the high outlay on welding work for assembling the housing surrounding the inner gas-conducting pipe and for mounting this housing on a cylinder head flange remain disadvantageous, since both contribute to increasing the costs of exhaust manifolds of this type. The required tightness of the exhaust manifold means that in the case of the known constructions, welding work of this type may not, however, be omitted.
It is, therefore, the object of the present invention to provide an exhaust manifold for mounting on a cylinder head of an internal combustion engine, said exhaust manifold being simple and cost-effective to produce, having a low mass and being able to be mounted on the cylinder head of the internal combustion engine in a simple manner.
According to the invention, this object is achieved by the features mentioned in claim 1.
The exhaust manifold according to the invention can be connected directly to the cylinder head by suitable fastening means, for example screws. In order to achieve a seal between the exhaust-gas collector housing and the cylinder head, just one sealing device is necessary between the exhaust-gas collector housing and the cylinder head, and costly welding work can be omitted.
The exhaust-gas collector housing can advantageously expand with respect to the cylinder head and can execute a corresponding movement, with the result that costly constructions having sliding flanges or the like can be avoided.
One particular advantage of the exhaust manifold according to the invention is the low degree of deformation required, as a result of which very thin metal plates having a correspondingly low mass can be used. This leads to very low material and production costs and to an extremely small amount of heat being removed from the exhaust gas. Furthermore, the exhaust manifold according to the invention has the advantage of requiring a relatively small amount of space in the engine compartment of a motor vehicle.
If, in one advantageous development of the invention, a flange is arranged between the exhaust-gas collector housing and the cylinder head, then an even better sliding movement of the exhaust-gas collector housing with respect to the cylinder head is possible on account of said housing possibly undergoing thermal expansion. In addition, this advantageously enables the cylinder head to be uncoupled from the exhaust-gas collector housing.
In a further advantageous refinement of the invention, a gas-conducting channel can be arranged in the exhaust-gas collector housing. This produces an exhaust manifold having air gap insulation, which exhaust manifold removes relatively little heat from the exhaust gas owing to the thin walls of the gas-conducting channel and the air gap between the exhaust-gas collector housing and the gas-conducting channel. This prevents the exhaust-gas temperature from dropping and results in better light-off performance and efficiency of a catalytic converter arranged in the exhaust pipe adjoining the exhaust manifold.
Furthermore, when a gas-conducting channel is used, an exhaust-gas collector housing consisting of cost-effective structural steel which can easily be deformed is advantageously used, since said housing is thermally less severely stressed.
Also in this embodiment, a flange can be arranged between the exhaust-gas collector housing and the cylinder head, which flange permits the better sliding movement of the exhaust-gas collector housing with respect to the cylinder head.
In the case of all of the embodiments, a low degree of deformation arises, which leads advantageously to thin metal plates and therefore to the individual components having very small masses.
In a further advantageously embodiment of the invention, provision can be made for the gas-conducting channel to be provided, on its side facing the cylinder head, with a circumferential collar which, in the assembled state, is at least indirectly wedged between the exhaust-gas collector housing and the sealing device, movements caused by the effect of heat being possible between the gas-conducting channel and the sealing device.
This results in a very simple fastening of the gas-conducting channel, but displacement thereof in the plane of the cylinder head remaining possible, however, and, at the same time, movement thereof perpendicularly with respect to this plane and clattering possibly caused thereby being prevented.